How can I get/set the current margins of a page?

Hi everybody,
I have somp problems handling new page jumps with the printer object.
I mean, I know how to get the paper size, and I know how to keep track of the lines I am printing, but the page jump is always too late, because the actual print area is smallet than the true paper size.
Can anybody tell me how to get or set the printable area of a page?
Thanx